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引用本文:王对兴,管琪,高万里,李春麟,张聚全,赵凯华. 浙东天台地区早白垩世花岗岩及暗色包体锆石U-Pb年龄、地球化学及其成因[J]. 中国地质, 2019, 46(6): 1512-1529.
WANG Duixing,GUAN Qi,GAO Wanli,LI Chunlin,ZHANG Juquan,ZHAO Kaihua. Zircon U-Pb age,geochemistry and genesis of the Early Cretaceous mafic enclaves and granites in Tiantai area,eastern Zhejiang Province[J]. Geology in China, 2019, 46(6): 1512-1529(in Chinese with English abstract).
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浙东天台地区早白垩世花岗岩及暗色包体锆石U-Pb年龄、地球化学及其成因
王对兴1, 管琪1, 高万里2, 李春麟2, 张聚全1, 赵凯华3
1.河北地质大学资源学院, 河北 石家庄 050031;2.中国地质科学院地质力学研究所, 北京 100081;3.河北省地矿局第九地质大队, 河北 邢台 054000
摘要:
在华南东部浙闽沿海一带普遍发育有大量晚中生代花岗质岩体及其中的暗色包体,这些岩体被认为是大规模壳幔相互作用和岩浆混合作用的产物。本文对浙东天台地区白鹤岩体中的寄主花岗岩及其中发育的暗色包体分别进行了LA-ICP-MS锆石U-Pb定年和详细的岩石地球化学研究,其锆石U-Pb年龄分别为(120.4±1.2)Ma和(120.6±1.1)Ma,属浙东燕山期侵入活动集中的早白垩世中晚期产物。岩石地球化学特征显示,寄主花岗岩为高硅、富碱、弱过铝质的高钾钙碱性花岗岩,具有较强的Eu负异常,富集Rb、Th、U、K,并有Sr、Ba、P、Ti、Nb、Ta等元素的亏损,岩石成因为高分异I型花岗岩;暗色包体多为低硅、富钠、偏铝质低钾拉斑玄武系列岩石,轻稀土富集、重稀土亏损,并具有弱的Eu正异常。锆石Hf同位素组成表现出不同物质来源(壳幔混源)花岗岩类岩石的特点。综合年代学及岩石地球化学特征,认为浙东地区早白垩世I型花岗岩及其暗色包体是在燕山期弧后碰撞伸展引张的构造背景下,由底侵的幔源岩浆与其诱发熔融的深部壳源岩浆经混合后,经过一定程度的分异演化,最后定位于浅成环境的产物。
关键词:  早白垩世  LA-ICP-MS锆石U-Pb测年  岩石地球化学  地质调查工程  天台地区  浙东
DOI:10.12029/gc20190617
分类号:P581;P595
基金项目:中国地质调查局项目(1212011121068)、国家自然科学基金项目(41602028,41602040)和河北地质大学博士科研启动基金项目(BQ201517)联合资助。
Zircon U-Pb age,geochemistry and genesis of the Early Cretaceous mafic enclaves and granites in Tiantai area,eastern Zhejiang Province
WANG Duixing1, GUAN Qi1, GAO Wanli2, LI Chunlin2, ZHANG Juquan1, ZHAO Kaihua3
1.College of Resources, Hebei GEO University, Shijiazhuang 050031, Hebei, China;2.Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;3.No.9 Geological Party, Bureau of Geology and Mineral Resources Exploration and Development of Hebei Province, Xingtai 054000, Hebei, China
Abstract:
A large number of Late Mesozoic granitic plutons with dark enclaves are widespread in the coastal area of Zhejiang and Fujian Province. They are considered to be the product of large-scale crust mantle interaction and magma mixing. In this paper, the authors conducted the LA-ICP-MS U-Pb dating and obtained whole-rock geochemical data of the host granites and dark enclaves of Baihe intrusion in Tiantai area, eastern Zhejiang Province, with the purpose of exploring the geochronology, petrogenesis and tectonic implications. The results obtained show that the U-Pb zircon ages of the host granite and dark enclaves are(120.4±1.2) Ma and(120.6±1.1) Ma, respectively. They are products of the Early Cretaceous Yanshanian intrusive activities in eastern Zhejiang in a syncollisional-postcollisional environment. Geochemical analyses show that the host rocks are high-potassium calc-alkaline Itype granite, with enriched SiO2, total alkalis, and weakly-peraluminous nature; they are enriched in Rb, Th, U and K, and depleted in Sr, Ba, P, Ti, Nb and Ta, with strong negative Eu anomaly. The dark enclaves belong chemically to partial alumina low-potassium tholeiite series, with lower SiO2, enriched sodium, enriched LREE, relatively depleted HREE, and weak positive Eu anomaly. The Hf isotope composition of zircons from host granite and dark enclaves are all indicative of mixing of crustal and mantle materials. Based on the geochronological and geochemical data, the authors hold that the Early Cretaceous I-type granites and their dark enclaves in eastern Zhejiang were generated by mixing of mantle-derived basic magma and its induced crustal felsic magma in an extension environment which followed the Yanshanian arc-back collision.
Key words:  Early Cretaceous  LA-ICP-MS zircon U-Pb dating  geochemistry  geological survey engineering  Tiantai area  eastern Zhejiang Province